1. Field of the Invention
This invention relates to electro-optical sensor systems and, more particularly, to a staring sensor apparatus capable of simultaneously covering up to 360.degree. azimuthal field of regard.
2. Description of the Related Art
Optical sensors are easier to design when the field of view is narrow. Wide field sensors have greater aberration problems, including coma, chromatic aberrations, and non flat focal planes. Some approaches to wide angle sensors include designs which preclude the use of normal flat focal plane arrays (FPAs). To mitigate these problems, scanning sensors are often used to cover wide fields using narrow field optics. Scanning systems sensitivity is generally low compared to staring system sensitivity. This causes the designer to sacrifice dwell time and revisit time desires. The requirements for sensitivity are then met by using larger and larger optics. The resulting systems are heavier and more costly.
When fields of regard approach and exceed 180.degree. using conventional optics, the optical system is often called a "fish eye" or "all sky" lens. This concept uses a family of lenses generically related in that they provide a wide angle of coverage around a hemisphere orthogonal to the prime axis.
The wide field sensors in the class pertinent to this patent application are generally designed to observe a cylinder whose sides are parallel to the prime axis of the optics. The present invention could be considered to fall within a subclass within this class, i.e. panoramic lenses. The valid elevation angle of the optics is constrained to be close to the horizon. The view directly in front of the optics is obscured. The problem with current optical systems providing panoramic views is that designers have been unable to combine this toroidal view, a conventional FPA, and a staring sensor. For a large set of applications, this "staring sensor" type is the best option from the standpoint of size, weight, sensitivity, and cost.